Combining catalytic reaction and product separation in the same reactor can improve the conversion and selectivity for many equilibrium-limited reactions, reduce capital costs and also enhance catalyst lifetimes.
Traditional catalytic distillation unit (CDU) technology combines a heterogeneous catalytic reaction and product separation in a single reactor. The heterogeneous catalyst acts as distillation packing as well as a catalyst for the reaction. Although the concept of carrying out the reaction and separation in a single reactor is not new, the problem of high-pressure drop when catalyst pellets are placed in a distillation tower has delayed the actual commercial utilization of this technology. A breakthrough came in 1980 when Smith in Texas patented a method of placing catalyst particles in fiberglass bags, which subsequently are rolled in bundles with demister wire in between to provide a void space for vapor flow. This form of catalytic distillation packing is also known as “Texas tea bags.” Smith has a number of patents on the application of CDU including the production of methyl-tert-butyl-ether (MTBE) (U.S. Pat. Nos. 4,232,177; 4,307,254; and 4,336,407, which are hereby incorporated by reference for all purposes). The first commercial application of CDU was the production of MTBE by Charter Oil at their Houston, Tex., refinery in 1981. The success of the CDU technology for the production of MTBE has led to great interest in using CDU as a more general reaction technique.
There are a number of advantages of the CDU technology due to the combinations of reactions and distillation in a single column. Indeed, CDU is deemed to play a major role for the chemical and petroleum industry in the 21st century. Some of the major benefits for CDU include a reduction in capital costs, increased conversion for equilibrium limited reactions due to the continual removal of products via distillation, improved product selectivity, improved catalyst lifetime due to the reduction of hot spots and removal of fouling substances from the catalyst, and a reduction in energy costs due to the utilization of reaction heat for vaporization and distillation.
Not all catalytic reactions are suitable for carrying out in the CDU mode. Some of the key requirements for suitable reactions are that distillation must be a practical method of separating the reactants and products, the reaction must proceed at a reasonable rate at the temperature equivalent to the boiling point of the liquid mixture in the column, and the reaction cannot be overly endothermic.
Numerous references teach the oligomerization of olefins. For example, U.S. Pat. No. 6,025,533 to Vora, et al. (“Oligomer Production with Catalytic Distillation”) teaches production of heavy oligomers (C7+oligomers) from C4 paraffins and olefins by a combination of dehydrogenation and oligomerization. The process has at least one catalyst bed in the top of a distillation column for separating the oligomerization effluent of the dehydrogenation and oligomerization combination.
U.S. Pat. No. 5,276,229; to Buchanan, et al. (“High VI Synthetic Lubricants From Thermally Cracked Slack Wax”) teaches oligomerizing alpha-olefins produced from thermally cracked slack wax.
U.S. Pat. No. 5,015,361 to Anthes, et al. (“Catalytic Dewaxing Process Employing Surface Acidity Deactivated Zeolite Catalysts”) teaches oligomerization of propylene in two stages using ZSM-23 and ZSM-5 to form a low pour point, high cloud point product, followed by dewaxing.
U.S. Pat. No. 4,855,524 to Harandi, et al. (“Process For Combining the Operation of Oligomerization Reactors Containing a Zeolite Oligomerization Catalyst”) teaches combining the operation of a primary reactor that oligomerizes a C3-7 feed to gasoline range hydrocarbons and a high pressure secondary reactor that oligomerizes the effluent of the first reactor to make distillate or lubes.
U.S. Pat. No. 4,678,645 to Chang, et al. (“Conversion of LPG Hydrocarbons to Distillate Fuels or Lubes Using Integration of LPG Dehydrogenation and MOGDL”) teaches converting C2-4-paraffins to higher hydrocarbons by the combination of catalytic or thermal dehydrogenation of a paraffinic feedstock to produce olefins and conversion of olefins to gasoline and distillate boiling range materials in a low pressure oligomerization catalytic reactor and a high pressure oligomerization catalytic reactor.
A variety of patents disclose catalysts useful for oligomerization. For example, U.S. Pat. No. 5,453,556 to Chang et al. (“Oligomerization Process For Producing Synthetic Lubricants”) teaches an oligomerization process using a catalyst having an acidic solid with a Group IVB metal oxide modified with an oxyanion of a Group VIB metal.
U.S. Pat. No. 5,270,273 to Pelrine et al. (“Olefin Oligomerization Catalyst”) teaches an olefin oligomerization catalyst having a supported, reduced Group VIB metal oxide on an inorganic support, such as MCM-41.
U.S. Pat. No. 5,243,112 to Chester, et al. (“Lubricant Range Hydrocarbons From Light Olefins”) teaches oligomerizing an olefinic feedstock over a medium pore zeolite catalyst (HZSM-22).
U.S. Pat. No. 5,171,909 to Sanderson, et al. (“Synthetic Lubricant Base Stocks From Long-Chain Vinylidene Olefins and Long-Chain Alpha- and/or Internal-Olefins”) teaches oligomerization of long-chain olefins using certain acidic montmorillonite clay catalysts.
U.S. Pat. No. 5,146,022 to Buchanan et al (“High VI Synthetic Lubricants From Cracked Slack Wax”) teaches oligomerizing with a Lewis acid catalyst a mixture of C5-C18 or C6-C16 alpha-olefins produced from thermal cracking of slack wax.
U.S. Pat. No. 5,080,878 to Bowes, et al. (“Modified Crystalline Aluminosilicate Zeolite Catalyst and Its Use in the Production of Lubes of High Viscosity Index”) teaches oligomerization with a modified zeolite (ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, or ZSM-48).
U.S. Pat. No. 4,962,249 to Chen, et al. (“High VI Lubricants From Lower Alkene Oligomers”) teaches oligomerization of lower olefins with a reduced valence state Group VIB metal oxide on porous support. In one embodiment, a feedstock of lower olefins is contacted with surface deactivated, acidic, medium pore, shape selective metallosilicate catalyst under oligomerization conditions, then reacting the mixture with ethylene in contact with an olefin metathesis catalyst under metathesis conditions, then oligomerizing the metathesis product in contact with a reduced valence state Group VIB metal catalyst on porous support.
U.S. Pat. No. 4,542,251 to Miller (“Oligomerization of Liquid Olefin Over a Nickel-Containing Silicaceous Crystalline Molecular Sieve”) teaches oligomerization in the liquid phase using nickel-containing silicaceous crystalline molecular sieve catalysts to produce lube base stock.
U.S. Pat. No. 4,417,088 to Miller (“Oligomerization of Liquid Olefins”) teaches oligomerization of liquid olefins using intermediate pore size molecular sieves to produce lube base stock.
EP 791,643 A1 (“Lubricating Oils”) teaches a process for the production of lubricating oils having a viscosity index of at least 120 and a pour point of −45 C or less by oligomerizing a feedstock comprising one or more C5-18 1-olefins in the presence of an oligomerization catalyst comprising an ionic liquid.
U.S. Pat. Nos. 4,417,088; 4,542,251; 4,678,645; 4,855,524; 4,962,249; 5,015,361; 5,080,878; 5,146,022; 5,171,909; 5,243,112; 5,270,273; 5,276,229; 5,453,556; and 6,025,533 are hereby incorporated by reference for all purposes.
It would be advantageous to provide a process for oligomerizing olefins to form lube base stocks. The present invention provides such a process.